學物理，也學AI。給國高中生與上班族的科學與 AI 筆記Learn physics. Learn AI. Science and AI notes for students and office workers.
「咖啡喝越多越矮」的調查圖，證明不了咖啡害人長不高。一起變化只叫相關，要說因果，得用控制變因的公平實驗。A chart showing coffee drinkers are shorter cannot prove coffee stunts growth. Changing together is correlation. To show cause, you need a fair test with controlled variables.
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薔琵颱風帶來 10 級、甚至 17 級強陣風，全台上千件招牌災情。風速只快一倍，動能卻變 4 倍，因為動能和速率的平方成正比。Typhoon gusts reached level 10, even level 17. When wind is twice as fast, its kinetic energy is 4 times bigger, because kinetic energy depends on speed squared.
急轉彎時你滑向車門，不是被「離心力」往外推，而是身體想直走、車子往內轉。讓車轉彎的是指向圓心的靜摩擦力。In a sharp turn, no force throws you outward. Your body wants to go straight while the car turns in. Static friction toward the center makes the car turn.
特斯拉宣稱新 Roadster 0→60 mph 只要 0.81 秒，約 3.4 g。但輪胎摩擦力上限只有約 1 g——多出來的力從哪來？Tesla claims its new Roadster can go from 0 to 60 mph in 0.81 seconds. Tires alone would need about 2.7 seconds. The extra push is claimed to come from suction fans and cold-gas thrusters.
